The present invention relates to a device comprising nickel silicide including iridium for use in ultra-shallow junctions with high thermal stability and a method of manufacturing the same, and, more particularly, to an integrated circuit device including a nickel silicide on a silicon substrate wherein iridium is utilized as an interlayer in the fabrication of the silicide.
Titanium silicide and cobalt silicide are each currently being used in salicide manufacturing processes to produce metal oxide semiconductor (MOS) transistors. Titanium silicide has a disadvantage in that it is difficult to transform the silicide to a low resistivity C54 phase when the polysilicon line width is reduced. Cobalt silicide has the disadvantage of a high silicon (Si) consumption rate to form cobalt disilicide. Therefore, it is difficult to apply cobalt silicide directly on an ultra-shallow source/drain area. Moreover, a reduction in the junction depth requires a very flat interface between the silicide layer and the silicon active layer.
Nickel silicide is a candidate material for use in future complementary metal oxide semiconductor (CMOS) device generations. In addition to the advantages of low resistivity and reduced Si consumption of the monosilicide, very low junction leakage has been demonstrated in conjunction with plasma doped ultra-shallow junctions. The major drawback to using nickel silicide is its poor thermal stability at temperatures above 650xc2x0 C. Heretofore, this limitation has prevented the use of nickel silicide in typical CMOS applications.
Nickel silicide is more suitable for ultra-shallow junction applications than titanium silicide and cobalt silicide because nickel monosilicide (NiSi) consumes only 1.83 Angstoms (xc3x85) of Si per xc3x85 of nickel (Ni) as compared with 3.64 xc3x85 of Si per xc3x85 of cobalt (Co) needed to form CoSi2. However, NiSi is not stable at temperatures higher than 700xc2x0 C. In particular, the NiSi further reacts with Si to convert to NiSi2, and at higher temperatures agglomerates to isolate islands within the film. Because future advanced integrated circuit (IC) processes will involve high temperatures, it is important to establish a method to form a silicide on an ultra-shallow junction which will be stable at temperatures of about 800xc2x0 C. or higher.
Adding platinum (Pt) to improve the thermal stability of nickel silicide has been discussed. However, it has been observed that electrically active defects in N-type Si were induced by the addition of Pt.
Accordingly, there is a need for a method to form a silicide layer on an ultra-shallow junction having a junction depth less than 400 Angstroms, while maintaining the junction integrity and stability of the silicide layer at temperatures of 800 degrees Celsius and greater.
The present invention provides a nickel silicide film having improved stability due to the addition of iridium into the metal film before the silicidation reaction. The stability of the resulting nickel silicide is much improved and facilitates use of the nickel silicide in ultra-shallow junctions at temperatures of 800 degrees Celsius or more. In particular, the thermal stability of a nickel silicide film is improved by adding an ultra thin metal interlayer before nickel deposition. With the incorporation of an interlayer of iridium it is possible to improve the thermal stability of nickel silicide films to withstand process temperatures sufficient for integration in 0.1 xcexcm technology process flows and beyond. In particular, the iridium interlayer regulates the flux of the Ni atoms through the iridium/nickel/silicon alloy layer formed from the reaction of the iridium interlayer with the nickel and the silicon so that the Ni atoms reach the Si interface at a similar rate, i.e., without any orientation preference, so as to form a uniform layer of nickel silicide.
Two types of wafers were used for this study. Wafers for measuring the silicide sheet resistance and crystalline structure were patternless p-type (100) Si wafers. In the preferred embodiment, the silicon substrate comprises an amorphous silicon substrate or a (100) silicon substrate. The patternless p-type wafers were subject to a pre-metal dip in a dilute buffered hydrofluoric acid (HF), a de-ionized (DI) water rinse and spin drying before being loading into an e-beam evaporation chamber. Nickel and the interlayer metal were deposited by sequential e-beam evaporation. The thickness of iridium (Ir) deposited was in the range of 5 Angstrom (xc3x85) to 20 xc3x85. The nickel (Ni) thickness was in the range of 60 xc3x85 to 130 xc3x85. The rapid thermal anneals were performed in an argon (Ar) ambient for 60 seconds (sec) at temperatures in the range of 300xc2x0 C. to 900xc2x0 C. The sheet resistance of each silicide film was determined by a four-point probe. The film structure was analyzed by a Philips Analytical x-ray diffraction system in a low resolution, xe2x80x9cphasexe2x80x9d identification mode: the sample was fixed and only the detector moved. Due to the close lattice mismatch between NiSi2 and the Si substrate, the phase was also examined by high-resolution x-ray diffraction.
A second type of wafer was used for measuring the reverse leakage on ultra-shallow junctions. The wafers were first oxidized and processed through standard photolithography and etch steps to form 200 xcexcmxc3x97200 xcexcm windows through a thermal oxide. After a 35 xc3x85 sacrificial oxide was grown, PN junctions were formed in the window areas by a plasma doping technique. N+/P junctions were formed by phosphorus doping on p-type wafers using a gas mixture of PH3/He. P+/N junctions were formed on n-type wafers by boron doping using a gas mixture of B2H6/He. An inductively coupled plasma was generated in a region above the wafer surface while negative voltage pulses of 1.0 to 1.5 kV amplitude and 50 to 100 xcexcs pulse width at frequencies of about 1 kHz were applied to the wafer through the chuck. Activation was achieved by a two-step rapid thermal anneal (RTA) anneal where recrystallization was performed at 800xc2x0 C. followed by a spike anneal at 1050xc2x0 C. The sacrificial oxide was then removed with a HF solution. The junction depths determined by secondary ion mass spectrometry (SIMS) were about 40 nm.
In order to avoid edge effects due to the removal of the sacrificial oxide, a plasma enhanced chemical vapor deposition (PECVD) oxide layer was deposited and a smaller window of 100 xcexcmxc3x97100 xcexcm was formed in the center of the previous window. The silicide was formed only in this 100 xcexcmxc3x97100 xcexcm region. Therefore, this technique of measuring reverse leakage was sensitive to modulation, spiking, or faceting at the interface between the silicide and the silicon. After the silicide formation, the unreacted metal films deposited on the oxide surfaces were removed in a solution of sulfuric acid and hydrogen peroxide at 140xc2x0 C. The backside oxide was removed by a HF solution before the leakage measurement. The current-voltage characteristics were measured with a HP 4156 semiconductor parameter analyzer.
Accordingly, an object of the present invention is to provide a nickel silicide film having improved thermal stability.
Another object of the present invention is to provide a nickel silicide film fabricated with the use of an iridium interlayer.
Yet another object of the present invention is to provide a nickel silicide film for use in ultra-shallow junctions having a junction depth of approximately 400 Angstroms, while maintaining the junction integrity and stability of the silicide layer at temperatures above 800xc2x0 C.